Wnt signalling: pathway or network?

Members of the Wnt family of secreted glycoproteins participate in many sig nalling events during development. Recent findings suggest that Wnt signals can sometimes play a permissive role during cell-fate assignment. Wnt prot eins have been shown to interact with a number of extracellular and cell-su rface proteins, whereas many intracellular components of the Wnt-signalling pathway are also invoked in other cellular functions. The consequences of Wnt signalling can be affected by members of the MAP kinase family. These o bservations suggest that the future understanding of Wnt signalling may req uire models that are based on a signalling network rather than a single lin ear pathway.